1. Technical Field
The present disclosure relates to improvement of image quality, and more particularly to a method and a device for processing an image signal, and a display system including the image processing device.
2. Discussion of the Related Art
Techniques for the transient improvement of an image signal increases clarity of the image by increasing sharpness and decreasing edge transition time. When the transient improvement technique is applied to a luminance signal, the technique is referred to as a Luminance Transient Improvement technique.
Typically, the transient improvement technique is used to make the image look sharper by decreasing transition time.
FIGS. 1A through 1E are waveform diagrams illustrating signals according to a conventional image quality improvement process.
FIG. 1A illustrates an image signal to be inputted to an image quality improvement device.
The image quality improvement device generates first and second derivative signals of an image signal. The first and second derivative signals are shown in FIGS. 1B and 1C, respectively.
The image quality improvement device generates a calibration signal shown in FIG. 1D by multiplying the first derivative signal by the second derivative signal. A sharpened image signal shown in FIG. 1E is generated by summing the image signal shown in FIG. 1A and the calibration signal shown in FIG. 1D.
The sharpened image signal shown in FIG. 1E has a short transition time compared with the image signal shown in FIG. 1A, but the sharpened image includes overshoot and undershoot. The overshoot and undershoot may make the image clear but may also degrade image quality by distorting the original image. As gain is increased, the overshoot and undershoot become larger.
Edge represents the portion of an image signal where there is a relatively large difference between pixel levels. Overshoot and undershoot occurring at an edge having a low slope may make the image clearer. However, when overshoot and undershoot occur at an edge having a rapid slope, image distortion caused by the overshoot and undershoot outweighs the added image clarity.